Gas venting in the manufacture of chilled rolls

ABSTRACT

In the casting of iron base rolls wherein multiple chiller sections are employed for effecting a hard roll surface; as the molten metal rises in the mold, combustion gases and air are entrapped between the rising metal and the chiller surface. These gases are vented by use of an inexpensive, thin, spacer element between the interfaces of the chiller sections. The spacer element may take the form of a continuous permeable material or of discreet spacers. In the latter instance, it is not necessary that the spacers be composed of permeable material and may, for example, be made of metal.

States net [191 Souers 1 Dec. 3, 1974 [54] GAS VE TI I TH M U U OF1,921,729 8/1933 Charman 249/201 2,133,829 10/1938 Ogden CHILLED ROLLS2,431,879 12/1947 Mebs [75] In entor: G rg uers, Min ral City,'02,453,643 11/1948 Schmertz 164/412 x [73] Assignee: United States SteelCorporation,

Pittsburgh, Pa. Primary ExaminerAndrew R. Juhasz Assistant Examiner-JohnS. Brown v [22] Filed 1972 Attorney, Agent, or FirmArthur J. Greif [21]Appl. No.: 310,722

Related US. Application Data ABSTRACT Continuation of 141,863. y 1971,In the casting of iron base rolls wherein multiple abandonedchillersections are employed for effecting a hard roll surface; as the moltenmetal rises in the mold, com- [52] US. Cl. 164/127, 164/355 bustiongases and air are entrapped between the rising [51] Il lt. Cl 322d 15/00metal d the chiller surface These gases are vented [58] Field of Search249/80, 111, 197, 201, by use of an inexpensive, thin Spacer element249/202; 164/122 133, tween the interfaces of the chiller sections. Thespacer 412 element may take the form of a continuous permeable materialor of discreet spacers. In the latter instance, it [56] References andis not necessary that the spacers be composed of per- UNITED STATESPATENTS meable material and may, for example, be made of 233,315 10/1880Barr .1 164/373 metal- I 795,643 7/1905 Newingham 164/373 933,996 9/1909Lewis 164/373 3 Chums 5 Drawmg Flgures GAS VENTING IN THE MANUFAC FCHHLLED ROLLS This is a continuation, of application Ser. No. 141,863,filed May 10, .971 and now abandoned.

This invention relates to an improved method forventing gases during thecasting of iron rolls.

Of all the steel ingots produced today, greater than 99 percent areprocessed further by being passed through either cast iron or cast steelrolls. Iron base rolls differ from steel base rolls principally in theircarbon content, the steel roll containing up to about 2.5 percentcarbon, whereas the iron roll contains carbon in greater amounts. Bothtypes of rolls are produced by the bottom pour swirl method, with themold in the vertical position. The hot metal enters at the bottom of thedragneck through a gate which is placed tangentially to the periphery ofthe neck. This placement imparts a vigorous spin or swirl to the metalas it enters the mold. The spinning action throws the denser, purermetal to the surface, thus ensuring a cleaner working face. The lessdense, dirtier metal is concentrated in the center of the rising metaland is subsequently carried to the top of the sinkhead. Iron base rollsare cast in a chill type mold, in which the neck is cast in sand but thebody of the roll is formed by a heavy-walled cast iron cylinder called achill. The chill, as its name implies, serves to cool the molten ironquickly, thereby producing a hard surface containing a minimum ofgraphite. Chill molds are of two types: the one piece chiller, with bodylengths of up to feet; and the multiple chill cylinder, in which a bodyof similar length is built up of chill sections, sometimes only a fewinches long. These chill sections are bored to a smooth finish and priorto casting are coated with a thin refractory dressing to avoid burn onof the hot metal. In the process of pouring the hot metal into the mold,gases are produced, both as a result of chemical reaction with therefractory dressing and as a result of evolution from the molten metalitself. These gases and the air entrapped by the rising liquid metal,must be efficiently vented to avoid surface defects in the casting.Previous attempts at venting such gases have taken the form of finelymachined saw cuts, either in the chill mold face or at the interfacebetween the various chill sections. In the former instance, these sawcuts are coated over by the refractory dressing which is permeable, andthus serves as channels for the gas to escape. This method has beenfound to be unsatisfactory in a number of instances, since the rapidlypoured molten metal tends to dislodge the dressing and enter the saw cutchannel, thus producing a fin of metal at the surface, which in turnwill cause a tear" or crack in the casting during the contraction stageof the solidifying process. Similarly formed fins also result when thesaw cut channels are employed in the interface between chill sections.In addition to the expense and difiiculty in making such saw cuts, bothmethods suffer from additional problems in that hot spots are formed atthe air gap or at the thicker refractory layer, where the hot liquidmetal is not in virtually direct contact with the metal chill. Thisinvention is therefore directed to a method for overcoming thesedifficulties, and eliminating the need for such critical machining withits corresponding excessive expense, by placing an inexpensive andexpendable, thin spacer element between the various chill sec-- tions.

The objects and advantages of, the invention will be better understoodby reference to the following description and drawings in which:

FIG. 1 is a cross-section of a roll mold; and

FIGS. 2 through 5 are sectional views of the top of a chill, depictingvarious types of spacer elements which may be employed.

Referring to FIG. 1, hot liquid metal is poured through the spout 1 andinto gate 2, which is set tangential to the periphery of neck 3. Themetal is poured rapidly so as to set up the vigorous spin referred toabove and to avoid steep thermal gradients in different parts of theroll, thereby preventing hot tears at such gradient points. The hotmetal rises through the mold and contacts the chills 4 and 5, promotinga hard, refined outer skin at the contact areas. The metal thereafterrises through neck 6 and into the sinkhead area 7.

If machined channels are employed in the mold face, the gases willpenetrate the refractory dressing covering the channels and exit throughthe permeable sand at 8. On the other hand, if channels are cut in theinterface between the chills (illustrated by heavy, dotted line at 9),the gases will be vented at those points. In both instances, themachining required to effect the critical depth of cuts is expensive andtedious. Small deviations in the depth of these cuts, result in eitherinsufficient venting or in the production of fins and hot spots. Thus,if the channel is too shallow, the gases will not have a sufficient areafor escape; whereas if the channel is too deep, hot metal will eitherenter the channel and produce a fin, or will not be chilled sufficiently(due to lack of contact with the metal chill) and produce a soft spot onthe roll surface, due to the precipitation of graphitic carbon. Equallyimportant, the sharp edges of the saw cuts provide areas for excessivebuild-up of the refractory wash, thus providing additional surfacedefects.

The instant method overcomes these various difficulties by interpositionof an inexpensive, expendable spacer element between the chillinterfaces 9. FIGS. 2 through 5 show the top of a chill interface,depicting, in section, a few of the embodiments which may be employedwithin the scope of the instant invention. In a preferred embodiment, asshown in FIG. 2, thin wires 10 are interposed between the chills toprovide a large venting area with a small gap, thus considerablyreducing the possibility of intrusion of molten metal into the ventareas (shown by arrows). It should be understood that for purposes ofthis invention, the term wire is not limited to strand material ofcircular cross-section, but refers to any such material of variouspolygonal cross-sections.

In a specific application, soft copper wires, 0.030 inches in diameterwere placed radially (as shown) at a distance of about six inches apart.The weight of the top chill and the top portion of the flask wassufficient to compress the wires to a gap of about 0.01 inches. Anadditional benefit may be derived in the use of an easily compressiblematerial, such as soft metal, in that the compression exerted by the topportions of the flask provides a positive, equal venting around theentire circumference of the chill, thus overcoming any possible misfitin the interface between the chills. Thus, if the interface fit betweenthe chills is not perfectly flat (as is generally the case) the morecontiguous portions would tend to compress the wires to a greater extentthan those interface portions in which some misalignment exists.

FIG. 3 shows the use of sheet material 11 to effect the desired ventingand FIG. 4 shows the use of a continuous porous gasket material 12. FIG.5 illustrates the use of labyrinth type spacer element, which provides amore indirect venting capability, thereby further inhibiting theintroduction of molten metal into the venting areas. Any refractory typematerial such as metals or ceramics may be employed in the gaskets. Inall instances, it is desirable to employ a material with sufficientyield qualities to provide a more uniform vent gap spacing, byaccommodation to irregularities in the chill mold surfaces in contactwith the spacer element. To provide adequate venting and avoid theoccurrence of finning, the final vent gap, after compression of thespacer element should preferably be between about 0.01 and 0.02 inches.

I claim:

I. In the casting of iron base rolls wherein the molten metal whichforms the roll body is poured through a gate set tangential to theperiphery of the neck portion of the roll, said metal being pouredrapidly to achieve a vigorous spin and thereby avoid steep thermalgradients in different parts of the roll, wherein said molten metal iscontacted with a heavy-walled cast iron chill which serves to quicklycool said molten metal, thereby producing a uniformly hard roll surfacecontaining a minimum of graphite, said chill comprising at least twoseparate, cylindrical, vertically aligned chiller sections, therebyresulting in the production and entrapment of gases which aredeleterious to the production of a smooth roll surface, the improvementwhich comprises, interposing discrete, removable spacer elements aroundthe circumference of said roll body, between the horizontal interfacesof said chiller sections to effect a gap therebetween for effectivelyventing said deleterious gases; said gap being small enough tosubstantially prevent the ingress of molten metal, said spacer elementsbeing of a dimension thicker than the desired gap opening and composedof a material which is suffciently yieldable to provide the desired gapopening on being compressed during the set up of the mold.

2. The method of claim 1 wherein said yieldable material is a metal inthe form of a wire.

3. The method of claim 1 wherein said desired gap is from about 0.01 toabout 0.02 inches.

1. In the casting of iron base rolls wherein the molten metal whichforms the roll body is poured through a gate set tangential to theperiphery of the neck portion of the roll, said metal being pouredrapidly to achieve a vigorous spin and thereby avoid steep thermalgradients in different parts of the roll, wherein said molten metal iscontacted with a heavy-walled cast iron chill which serves to quicklycool said molten metal, thereby producing a uniformly hard roll surfacecontaining a minimum of graphite, said chill comprising at least twoseparate, cylindrical, vertically aligned chiller sections, therebyresulting in the production and entrapment of gases which aredeleterious to the production of a smooth roll surface, the improvementwhich comprises, interposing discrete, removable spacer elements aroundthe circumference of said roll body, between the horizontal interfacesof said chiller sections to effect a gap therebetween for effectivelyventing said deleterious gases; said gap being small enough tosubstantially prevent the ingress of molten metal, said spacer elementsbeing of a dimension thicker than the desired gap opening and composedof a material which is sufficiently yieldable to provide the desired gapopening on being compressed during the set up of the mold.
 2. The methodof claim 1 wherein said yieldable material is a metal in the form of awire.
 3. The method of claim 1 wherein said desired gap is from about0.01 to about 0.02 inches.